Scientists say 'debunked' theory may actually explain cause of autism: 'Not as far fetched as once thought'
- READ MORE: Trump Administration's astonishing autism promise
Autism might begin in the gut — not the brain.
A new study has found autistic children have [distinctly] different bacteria in their stomachs compared to kids without the condition.
The researchers say these changes to the microbiome - a network of bacteria that regulate digestion and other processes - lead to changes in parts of the brain associated with behavior and learning.
Diet and other environmental exposures in the womb have been linked to harmful microbiome changes in babies.
The team noted autistic children were also more likely to have had mothers who used antibiotics in pregnancy, suggesting use of the medications could have increased the risk of autism.
They compared stool samples and brain scans of children aged eight to 17 with autism compared to typically developing children in the same age group.
They found autistic children and teens had lower levels of certain metabolites - small molecules produced during digestion - than neurotypical children, causing their guts to produce less of the mood-regulating hormone serotonin.
The researchers believe these changes in the gut microbiome may lead to symptoms of autism like communication difficulties and behavioral issues.
This so-called 'gut-brain' connection theory has been suggested for decades as a potential autism cause but was thought to have been debunked.
Changes to the gut microbiome may help explain a rise in autism cases, acccording to a new study (stock images)
However, the new study injects life back into that theory by looking at stool samples and brain scans at the same time and homing in one particular sets of metabolites.
The team, from the University of Southern California, said the findings could lead to treatments targeting the gut 'while also hopefully alleviating some of the symptoms that are the most uncomfortable for [autistic children],' like bloating and constipation.
However, they cautioned more large-scale, definitive research is still needed.
Lisa Aziz-Zadeh, lead study author and professor at the Brain and Creativity Institute at the University of Southern California, said: 'We demonstrated that gut metabolites impact the brain, and the brain, in turn, affects behavior. Essentially, the brain acts as the intermediary between gut health and autism-related behaviors.
'Previous studies highlighted differences in gut microbiomes and brain structures in autism, but our research connects the dots.'
The findings come as one in 36 children in the US have autism, adding up to just under 2million. In the early 2000s, that number was closer to one in 142, a four-fold rise.
Experts are working to uncover the causes of the increase, raising concerns over environmental factors like microplastics and pesticides.
They have also noted diagnostic changes have made it easier for doctors to spot the condition, especially in once overlooked groups like girls and adults.
The study, published Monday in Nature Communications, compared 43 children with autism to 41 neurotypical children from healthcare clinics in Los Angeles.
All participants were between eight and 17 years old, and the average age was 12.
About half of the autistic participants took medications like antidepressants, antipsychotics and stimulants for their behaviors. None of the neurotypical children took prescription drugs.
Researchers asked all of the children to stay away from antibiotics for a month and probiotics for two weeks, as both medications can alter the gut microbiome.
The study took place over the course of two days. On the first day, researchers gave the children behavioral assessments. On the second day, participants brought in stool samples and underwent MRI scans of their brains.
Parents were also asked to report which diet their children most closely followed: Standard American (high consumption of processed foods, red meat, poultry, eggs and dairy), Modified American (high consumption of whole grains, poultry, fish, eggs, dairy, vegetables, fruits and some processed foods), Mediterranean, Paleo, vegetarian, gluten-free, dairy-free, low FODMAP or other.
The researchers honed in on metabolites in participants' stool that followed the 'tryptophan pathway.'
Typtophan is an amino acid found in turkey, salmon, eggs, and seeds that breaks down into the metabolite serotonin, which is crucial for brain functions like emotional processing, social interaction and learning.
The researchers noted because more than 90 percent of the body's serotonin is produced in the gut, changes in gut health could influence serotonin levels.
Nerve cells in the gut then send signals to the brain, a phenomenon known as the gut-brain axis.
Children in the study with autism were more likely to have mothers who used antibiotics during pregnancy, which could have caused gut microbiome disturbances (stock image)
The team found children with autism had lower levels of typtophan metabolites than neurotypical children, resulting in lower serotonin levels.
This lead to higher rates of gastrointestinal issues like bloating and constipation and an increased prevalence of changes in areas of the brain responsible for social behaviors, leading to 'ASD symptomology.'
Aziz-Zadeh said: 'We know that children with autism have brain differences — certain parts of their brain are either less active or more active compared to typically developing children.
'We also know they often experience gastrointestinal issues, such as constipation, stomach pain and other digestive problems. Additionally, autism is associated with various symptoms, including repetitive behaviors and social difficulties.'
Along with diet, lower typtophan metabolites may also be caused by antibiotics disturbing the gut microbiome. The team found children with autism had a higher likelihood of their mothers using antibiotics during pregnancy.
The researchers wrote: 'Prenatal maternal antibiotic exposure has been shown to affect the maternal microbiome, which plays an important role in the fetal brain’s exposure to altered maternal microbial metabolites.
'This prenatal mechanism has been hypothesized to play a role in the etiology of ASD.'
However, the researchers cautioned 'out study is unable to demonstrate causality,' meaning it can't directly show metabolite levels cause autism.
Autism advocacy groups have also said the causes of autism are not fully understood and many experts suggest there isn't one specific cause.
There were several limitations to the study, including not looking at children under eight years old and having more boys than girls.
